In ourprevious installment of this series，，，，we met with a diverse array of Soft Corals and Gorgonians, including most of the species familiar to aquarists. Amongst these were a hodgepodge of ex-Scleraxonia, ex-Stolonifera, and ex-Alcyonacea genera, now all lumped together as a messy shrubbery of clades within the newly recognized order Malacalcyonacea. Before we leave this group, there is still one more major lineage to explore, composed of species that had previously formed the bulk of the Holaxonia Gorgonians, but also with a few unexpected surprises thrown in for good measure.
Recall that the former order Holaxonia was diagnosed by the composition of its axial skeleton, being made up of a protein called gorgonin that is frequently impregnated with varying forms of calcium carbonate—this is in contrast to the fused sclerites of the Scleraxonia or the crystalline calcite or aragonite of the Calcaxonia. For the most part, Holaxonia has proven to be more or less phylogenetically correct, albeit with a few minor (but interesting) exceptions.
这些异常值中最值得注意的是Dendrobrachia，一个缺乏硬化岩的细腻的深海戈贡人的小属；我们将在即将进行的巩膜环核探索中再次遇到。同样以该顺序（但无关）是Ideogorgia这是来自南非和阿根廷的一个晦涩的属，由于围绕其戈尔贡蛋白骨架的硬化物的奇特鞘，其亲和力长期以来一直不稳定。最后，在马拉卡尔环锥中有Acanthoaxis，2010年从喀麦隆描述；它的菌落缺乏硬化岩，可以构成或直立，这要归功于空心，跨载体的骨骼上覆盖着小刺的骨骼。
因此，我们至少有4个单独的实例，其中八八角素的产生出现在八光核心中。但是为什么这是？哪些因素可能有利于在这些不同的群体中的发展，而发展了数亿年。还是有可能出现在所有现代八角形的祖先中，然后随后在整个过程中丧生？这些戈贡蛋白的骨骼甚至是化学同源的，还是可能没有注意到的微妙差异？
The family-level classification of Holaxonia was always a bit sketchy and put a great deal of emphasis on the appearance of the axial skeleton’s hollow core. But this trait was often ambiguous and genera could convincingly be shuffled about seemingly at the whim of the taxonomist. Molecular data now indicates that the sclerites provide a far more useful diagnostic tool, and this is supported further when comparing their biogeography. So let’s get to know these dozen gorgonian families.
Plexauridae & Pterogorgiidae
在较旧的分类中，plexauridae是Holaxonian家庭中最多样化的家族，并且涵盖了广泛的地理和生态范围，但现在主要仅限于热带西大西洋，Plus Plus穆里西娅在东太平洋。这些属中的几个（Plexaura，，，，Pseudoplexaura，，，，Eunicea) are zooxanthellate andperiodically available to aquarists。
pterogorgiidae是一个新家庭，在热带西大西洋中有几个属，以及小（单型？）属Pinnigorgiain the West Pacific—this disjunct distribution is generally uncommon amongst octocorals, but we’ll see it again in Gorgoniidae.Pinnigorgiais often maricultured, and some of its relatives in the Atlantic (Pterogorgia，，，，Muriceopsis) have also been available, as these are all zooxanthellate (though the family also includes azooxanthellate species). The plexaurids and pterogorgiids are closely related and form a basal clade relative to the other families we’ll be discussing here, but neither is easily defined in terms of morphology.
Eunicellidae, Scleracidae, Plexaruellidae & Gorgoniidae
These families are all somewhat closely related and predominantly found in the Atlantic.Scleracis是一个深水加勒比属，具有较大的表面硬化症。Plexaurellais a zooxanthellate Caribbean genus, occasionally available to aquarists, best recognized by having sparsely branched colonies and polyps that retract into slit-like apertures—these were formerly confused with the plexaurids, but differ in having a heavily calcified axial skeleton and “butterfly sclerites”.
Gorgoniidae is a widespread group and is probably the most familiar. The fan-shaped species ofGorgoniaand its feathery counterparts inAntillogorgiaare both ubiquitous in the Caribbean, the latter often being水族员可用。但是这个家庭还包括一对奇特的扁平属，巴西的Phyllogorgiaand Chile’sPhycogorgia，再加上一个印度太平洋属，Pseudopterogorgia。The family is loosely defined by having relatively small surface sclerites and inclusions of carbonate hydroxylapatite in the axial skeleton.
Lastly, the eunicellids are an oddly schizophrenic group. On the one hand, there’sEunicella，，，，a common genus of Gorgonians in the Eastern Atlantic diagnosed by its distinctive “balloon-club sclerites”;另一方面，有Complexum，，，，an obscure tropical Western African genus of azooxanthellate Soft Corals. These seem like odd bedfellows, but the molecular data is unequivocal in supporting a close relationship for these genera, which goes to show just how malleable bodyplans can be in Octocorallia.
Paramuriceidae, Astrogorgiidae, Euplexauridae, & Anthogorgiidae
这些家庭在印度太平洋地区有些密切相关，并且主要是在印度太平洋地区发现的，尽管Anthogorgiidae实际上源自刚刚讨论过的大西洋家庭中。Anthogorgia caerulea是一种常见的水族馆出口，称为蓝莓Gorgonian（通常被错误地为aCalycigorgia) on account of its vibrant polyps, though it seldom thrives in captivity. Also in this family isMuricella plectana,一个大的扇形Bargibant P的物种ygmy Seahorse. The group is defined in part by having abundant sclerites in their polyps, such that they are unable to be withdrawn into the surrounding coenenchyme.
对于刺的息肉也可以说Acanthogorgia，，，，which is now included within the newly recognized Paramuriceidae. This family was split from its Atlantic counterparts, Plexauridae, and now accounts for the most diverse group of Gorgonians in the Indo-Pacific. Here we find just about every colony shape and size imaginable, from fans to bushes to sparse twigs or wires, usually with retractile polyps, but sometimes not. Remarkably, there’s also a small, cushion-like Soft Coral from the West Coast,血栓菌。One important morphological trait shared by most of these is the presence of “thornscale sclerites”，以及“collaret & points sclerites”在息肉中。
Astrogorgiahas long been associated with the paramuriceid genera, but it notably lacks thornscales and tends to have somewhat flattened branches.Euplexaurasuperficially resembles some of the Atlantic plexaurids in having a greatly thickened coenenchyme, but these azooxanthellate Gorgonians instead form a small sister group to the paramuriceids, though the absence of thornscales helps to distinguish these.
isididae
Most Indo-Pacific Gorgonians are azooxanthellate, which explains why so few of them are ever seen by aquarists, but Isididae is a major exception. This family has undergone a dramatic shift, as it formerly included a broad array of deepsea Bamboo Corals, now recognized as belonging to the Scleralcyonacea. All that remains of its original configuration isIsis hippuris，一种西太平洋物种peculiarly jointed skeletonof gorgonin nodes and calcareous internodes. But rather than the crystalline internodes seen in a true Bamboo Coral,Isis有一束方解石似乎是从高度修饰的硬化岩中得出的。现在也加入了印度太平洋的属Rumphellaand希克森拉，，，，both of which possess a more typical gorgonin axial skeleton, but all three otherwise share similarities in their colony shape and sclerite morphology, hinting at their unexpectedly close relationship.Rumphella aggregata有时可供水准主义者使用。
Keroeididae
This small family has always been a bit of an enigma. The axial skeleton is mostly gorgonin, but with an outer layer of sclerites, thus combining aspects of the old Holaxonia and Scleraxonia. These tend to be uncommon and restricted to moderate depths, and few have been investigated with molecular data. Of those that have, the aforementionedIdeogorgiahas been relocated to the Scleralcyonacea, while the type genusKeroeides仍然是我们一直在讨论的Gorgonian家庭中的孤立血统。ThelogorgiaandPseudothelogorgiamay also belong here (or they may not); these are equally obscure groups, the latter有时会发生在印度太平洋的珊瑚礁上。
Taiaroidae
奇怪的是，据称的Keroeididae姐妹团体是Taiaroa Tauhou，来自印度太平洋深海栖息地的Gargantuan孤立物种以前被归类为原始囊性。从表面上看，这是零有意义的，但是挖得更深入，这仍然没有任何意义。当然，这些谱系被数亿年的进化所隔开，并且在如此长的时间范围内可能会发生很多事情。必须假设Taiaroawere at some point more Gorgonian-like, but, much like inComplexumandThrombophytum，决定探索不同的形态学途径。剩下的原始囊属属仍然太鲜为人知，无法假设，但是这些属似乎不太可能密切相关。
Discophytidae
最后，简短提及Discophyton Rudyi， 这odd little encrusting speciesfrom the West Coast that, likeTaiaroaandComplexumand血栓菌，，，，appears to represent a Gorgonian that has lost its way. No doubt there will be many more of these discovered once molecular data is brought to bear on all of the poorly studied octocorals out there. One possible example that jumps to mind is New Caledonia’s gorgeous紫色神秘珊瑚。
And with that, we’ve at long last reached the end of the Malacalcyoncea (well, aside from all the small families that we’ve shamelessly ignored along the way). Next up will be its charismatic sister lineage, Scleralcyonacea, a group chock full of morphological oddities, stretching Octocorallia to its very limits.
关于作者
Joe Rowlett is the author of Indo-Pacific Corals and studies marine biogeography and speciation. He is a former aquarist and has written extensively for aquarium publications.
